Feline leukemia virus (FeLV) suppresses the immune system and results in various types of cancer and other chronic and debilitating diseases in cats. Signs of infection include gum disease, vomiting, diarrhea, weight loss, decreased appetite, lethargy, anemia and infections that are resistant to standard treatments. Although cats can remain apparently healthy for months or even years following infection, once signs begin, they are difficult to impossible to treat successfully.

FeLV is transmitted through direct contact with an infected cat, such as by mutual grooming, fighting or playing, or by sharing a food or water dish or litter box with an infected cat. The virus can spread from an infected mother cat to her kittens through the placenta or during nursing. Bite wounds are an especially effective method of transmission because there is a high level of virus in salvia of an infected cat.

Affected cats not yet showing signs of illness may shed the virus and be infective to other cats, making it vital never to bring a new cat into your household without testing for FeLV. Many cats appear to be perfectly healthy at the time of diagnosis another reason every cat should be tested for FeLV. Because the disease's lengthy incubation period may cause an infected cat to test negative for some time after exposure, the cat should be retested six weeks after possible exposure.

Even though a vaccine against feline leukemia virus has been available to cat owners since 1985, FeLV remains the leading infectious cause of illness and death in domestic cats. At this time, vaccination and preventing exposure to possible carriers are the only defenses against this devastating disease.

FeLV vaccination consists of two initial injections about three weeks apart with yearly boosters thereafter. It is highly recommended that cats be tested for FeLV before vaccination.